The present invention relates to the structure of a solid electrolytic capacitor, and more particularly to the shapes and forming methods of electrode terminals.
With the miniaturization of electronic equipment, the surface mount of solid electrolytic capacitors has been necessitated, and surface-mountable solid electrolytic capacitors of chip type have been often employed.
A solid electrolytic capacitor in the prior art (hereinbelow, called “related art 1”) includes a capacitor element, an anode terminal which is joined to the anode lead of the capacitor element, and a cathode terminal which is disposed at the outer periphery of the capacitor element through an electroconductive adhesive. The solid capacitor has its surroundings covered with a casing material, such as plastics material. Herein, the cathode terminal and the anode terminal are formed so as to be exposed along the surface of the casing material.
Besides, as electronic equipment have become smaller in size and higher in performance in recent years, still smaller sizes and still larger capacitances have been required of capacitors. In this regard, products of bottom electrode structure type have been developed, in each of which electrode terminals are fixed on the mounting surface of the product, whereby the internal structure of the capacitor is made efficient so as to enlarge the volume of a capacitor element more (refer to, for example, JP-A-2001-267180 and JP-A-2001-110676 which shall be respectively referred to as “related arts 2 and 3” below).
In the solid electrolytic capacitor of bottom electrode structure type, a cathode terminal and an anode terminal are provided only at the mounting surface of the product. A capacitor element is bonded with the cathode terminal by an electroconductive adhesive. An anode lead is connected to the anode terminal through an anode connection component. Welding, the electroconductive adhesive, or the like is employed for anode connection component and anode terminal connecting the adjacent ones of the anode connection line or lead.
The structure of the solid electrolytic capacitor of conventional surface mount type, however, has had the problem that large spaces are required for joining the capacitor element with the anode terminal and the cathode terminal, so the volume of the capacitor element cannot be made very large.
The reason therefor is that, since the anode terminal and the anode lead are joined in parallel, the space for leading out the anode terminal from the joined part of the anode to the exterior of the casing material is required. Also in the connection between the cathode terminal and the element, the space for leading out the cathode terminal from the joined part thereof to the exterior of the casing material is required. Since the spaces for leading out the anode terminal and the cathode terminal do not contribute to the capacitance of the capacitor, they have been minus factors for reducing the size of the capacitor and enlarging the capacitance thereof.
On the other hand, the recent solid electrolytic capacitor of bottom electrode structure type has had the problem that the reliability of electrical connections lowers. The reason therefor is that the anode connection component is used for relaying the connection between the anode lead and the anode terminal, so two places to be joined are provided. In the conventional surface mount type, anode connection is made in only one place between the anode lead and the anode terminal, so that the bottom electrode structure type is lower in the connection reliability.
Further, even the solid electrolytic capacitor of bottom electrode structure type requires the wet bumps, which will be referred to as “fillets”, hereinbelow, of a solder at terminal parts on the side surfaces of the product after being mounted on a substrate. In each of the solid electrolytic capacitor of the conventional surface mount type and that of the prior-art bottom electrode type, accordingly, the terminals are so arranged that, in order to form the fillets, parts of the terminals are exposed to the side surfaces of the product in the directions of the anode and the cathode so as to hold the wettability of the solder. That is, a terminal array in which the fillets are formed needs to be realized in the solid electrolytic capacitor.